Recent findings, notably that Aedes triseriatus mosquitoes orally infected with La Crosse (LAC) virus do not produce transovarially infected progeny until the second oviposition following the infectious bloodmeal, have made it mandatory to determine survivorship to the 2nd and subsequent ovipositions in order to assess the significance of horizontal amplification via vertebrates in endemic survival of the virus. Efforts will focus, therefore, on the development of trapping techniques to be used in estimating mosquito survival to mating, the first and subsequent ovipositions and the first and subsequent bloodmeals. The circumstances of human infection with LAC virus under urban and semi-urban conditions will also be investigated. Preiminary evidence indicates that a high proportion of human California encephalitis cases result from contact with Aedes triseriatus mosquitoes bred in discarded tires and other man-made containers.